Magnetic sensing systems are used in a wide variety of applications including, for example, determining the speed and direction of an object such as a rotating shaft. There are various methods of constructing the magnetic sensors of a magnetic sensing system. For example, a magnetic sensing system could comprise two separate magnetic sensors and a target (typically a structure having magnetic poles) that are arranged so that each of the two magnetic sensors produces an output signal as the target rotates or moves with respect to the magnetic sensors.
The two magnetic sensors may be spaced at a predetermined distance from one another so as to create a phase shift between their output signals. This phase shift can allow a designer (i) to use these output signals from the sensors to produce a higher resolution speed signal so that speed changes can be detected more quickly and (ii) to use the lead and lag information between the output signals from the two sensors in order to determine direction of rotation or movement of the target.
The phase shift between the outputs of two magnetic sensors is dependent on the spacing between the magnetic sensors and the spacing between the features of the rotating or moving target. Frequently, the target is a magnet, such as a ring magnet, with a plurality of evenly spaced magnetic poles. The magnetic sensors are usually contained in separate packages, which makes it very difficult for the magnetic sensors to be arranged in a manner so that their output signals meet specified phase shift requirements. The magnetic sensors must be very accurately manufactured and/or they must be dynamically adjusted so that their output signals meet the specified phase shift requirements. Otherwise, errors in the phase shift will lead to a miscalculation of the speed of the target and, if the phase error is large enough to allow the output signals to cross, to a miscalculation of the direction of the movement of the target.
Magnetic sensors are sometimes provided on the same integrated circuit and are spaced a certain distance apart. However, although this spacing may be good for one particular pole spacing, it will not be correct for another. One solution is to fabricate an integrated circuit for each different ring magnet. However, making a new integrated circuit for every new spacing is expensive.
The present invention overcomes one or more of these or other problems.